The present disclosure relates to a developing device for incorporation in an image forming apparatus such as a copier, facsimile machine, printer, or the like, and to an image forming apparatus incorporating such a developing device. More particularly, the present disclosure relates to a method of suppressing agglomeration and solidification of developer inside a developing device.
Conventionally, as image development methods using dry toner in image forming apparatuses relying on an electrophotographic process, there are known a one-component development method, which uses a one-component developer containing magnetic toner alone, and a two-component development method, which uses a two-component developer designed to electrically charge non-magnetic toner by use of magnetic carrier and which develops an electrostatic latent image on an image carrier (photosensitive member) with a magnetic brush formed on a developing roller and composed of magnetic carrier and toner.
In developing devices as mentioned above, as development operation proceeds, toner is consumed. To cope with that, a toner sensor for detecting the concentration (or amount) of toner is provided inside a developing device, and as toner is consumed through development, so much new toner is supplied. Here, with a two-component development method, toner and carrier need to be stirred and mixed sufficiently so that the toner is electrically charged up to a predetermined amount of electric charge. Also with a one-component development method, the toner existing inside the developing device and the newly supplied toner need to be mixed sufficiently so as to have an even distribution of electric charge.
To that end, according to a widely practiced method, a circulation passage for developer is provided inside a developing device, and the developer is circulated and transported, while being stirred and mixed, by a stirring/transporting member arranged inside the circulation passage which is in the form of a screw and which is composed of a rotary shaft and a helical blade. Specifically, in a developing device 101 as shown in FIG. 13, the interior of a developer container 102 is partitioned into a first transport passage 105 and a second transport passage 107 by a partition wall 103. Inside the first transport passage 105 and the second transport passage 107, a first spiral 109 and a second spiral 110 are rotatably arranged which transport the developer while mixing and stirring it.
The developer is transported, while being stirred, in the axial direction (in the directions indicated by arrows A1 and A2 in FIG. 13) by the first spiral 109 and the second spiral 110, and is circulated between the first transport passage 105 and the second transport passage 107 through developer passing portions 111a and 111b formed in both end parts of the partition wall 103. Thus, the first transport passage 105, the second transport passage 107, and the developer passing portions 111a and 111b form a circulation passage for developer inside the developer container 102.
There is also proposed a method for suppressing uneven distribution of developer in a developer passing portion. For example, in one known developing device, in a part, facing a developer passing portion, of a stirring/transporting member arranged farther from a developing roller, a paddle piece is provided along a rotary shaft, and this results in an improved developer transporting ability at the developer passing portion.
According to another known developing device provided with a developer discharge port, in a part of a stirring/transporting member facing a developer passing portion, a devoid portion devoid of a rotary shaft is formed, and this results in a reduced speed of developer colliding with a developer regulating member.